(a) Technical Field
The present invention relates to a force-torque sensor and a method for manufacturing the force-torque sensor. More particularly, it relates to a strain gauge type force-torque sensor and a method for manufacturing the force-torque sensor, which can measure multi-axial force and torque and save on manufacturing cost, and can overcome difficulties in attaching of a gauge and sensor defects and errors generated while attaching the gauge.
(b) Background Art
Automated facilities using robots have been widely used for various industries including precision welding and assembly processes on automobile assembly lines for years. To operate the robot-based automated facilities, it is necessary to measure and simultaneously feedback-control the location of a robot and the force and torque acting on the distal tools connected to robots. Particularly, to automatize complex and delicate tasks, position control and power control of robot arms and distal tools need to be simultaneously performed.
A position control method is mostly used for robots currently in use. However, as uses and the technology requirements of robots technologically progress to an environment which coexists with humans, service robots are expected to perform various tasks with a single device, and methods for driving these robots are being changed into practical force-controlling methods. Thus, interest in force-torque sensors that are being applied to robotic fields is gradually increasing as well.
A force-torque sensor detects external forces that act on the distal mechanism (e.g., distal tools installed on a robot arm) and plays an important role in the force-control robots, and therefore will be a core component service type robot in the future.
In particular, the measurement methods of typical force-torque sensors detecting external forces acting on robots and distal mechanisms may be roughly divided into methods which use deformation of an elastic body with a strain gauge, methods which use piezoelectric materials, and methods which use a Stewart platform mechanism with Linear Voltage Different Transforms (LVDT).
U.S. Pat. App. Pub. No. 2010/0000327 discloses a strain gauge type force-torque sensor. The sensor includes two flanges, each of which includes a flexible part and a connection part connected to the center thereof. The sensor measures a resistance variation using two or four strain gauges. In this case, strain gauges are located in a straight line on a plane of a lower flange, and the strain gauges are attached in orthogonal directions with respect to each axis. Also, U.S. Pat. App. Pub. No. 2008/0184819 discloses an electrostatic type sensor.
FIG. 6 is a view of a typical six axial force-torque sensor using deformation of an elastic body with a strain gauge. A tool connection part 10 is connected to a distal mechanism (tool), and a robot connection part 20 is connected to a robot arm or the like.
In the above force-torque sensor, the outer circumferential surface of the tool connection part 10 and the inner circumferential surface of the robot connection part 20 are integrally connected by three elastic beams 30, each of which is mechanically deformed by force or torque. Like a kind of torsion beam, the elastic beams 30 may be elastically distorted by force or torque. In this case, a plurality of strain gauges 32 are attached to the three elastic beams 30 to measure force and torque according to mechanical deformation of the elastic beams 30.
Such a typical six axial force-torque sensor has to be designed by expecting the change of the structure of the elastic beam, and has a structure in which the sensitivity of the sensor is determined according to the performance of the stain gauges attached to the elastic beams. The typical six axial force-torque sensor can measure both magnitude and direction of three-dimensional force components (Fx, Fy and Fz) and three dimensional torque components (Mx, My and Mz) when force and torque are applied. Since the force and torque components of each direction are mutually associated with each other, expensive silicon strain gauges are being used on the elastic beams to improve the accuracy of the measurement.
Although the six axial force-torque sensor mounted on a “wrist” portion of a robot shows sufficient sensitivity for measuring six axial force-torque in a signal structure, its elastic body (elastic beam) has a complicated three-dimensional structure, causing an increase in the manufacturing costs. Accordingly, it is necessary to develop a cost-saving and efficient force-torque sensor for distribution and popularization of robots.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.